Various systems are known in which operation of various subsystems of a vehicle can operate in different configuration modes so as to suit different conditions. For example, automatic transmissions can be controlled in sport, winter, economy and manual configuration modes in which the changes between gear ratios and other subsystem control parameters are modified so as to suit the prevailing conditions or the taste of the driver. Air suspensions are known with on-road and off-road configuration modes. Stability control systems can be operated at reduced activity so as to give the driver more direct control over the operation of the vehicle. Power steering systems can be operated in different configurations modes where the level of assistance is at different levels or varies in different ways. Vehicle transmissions can be switched to provide drive to different numbers of wheels. Also the locking or partial locking of differentials can be controlled to suit the prevailing driving conditions.
As the number of controllable systems increases, the driver will become faced with an increasing number of choices as to which configuration modes to select for each of the systems. Unless the driver is very experienced, this can become complicated and confusing.
Therefore, systems have been proposed in which the control of a number of the vehicle subsystems is coordinated by a central vehicle controller, which can be switched between a number of modes thereby controlling all of the subsystems in a coordinated way which is simple for the driver to control. Such a system is disclosed in EP-A-1355209.
Therein is described a vehicle control system arranged to control a plurality of vehicle subsystems each of which is operable in a plurality of subsystem configuration modes. The vehicle control system optimizes subsystem settings for the terrain and is operable in a plurality of driving modes in each of which it is arranged to select the subsystem configuration modes in a manner suitable for a respective driving surface.
However, although such a vehicle control system includes driving modes to coordinate the subsystems in order to optimize vehicle performance for the terrain, the driver will continue to have the ability to manually control individual subsystem functions from the passenger compartment. For example, the driver may have the ability to adjust the ride height of the vehicle available on the driving console. The ride height adjustment is a manual adjustment of the air suspension subsystem. It is possible that this manual request received by the suspension subsystem might be in conflict with a current or future command by the vehicle control system requiring a different suspension subsystem configuration. Known vehicle control systems might avoid this conflict by either restricting all manual command requests from the driver or overriding the vehicle control system. Unfortunately, these simple solutions often result in a complete bypass of the vehicle control system and fail to take advantage of the benefits associated with optimizing for the terrain. Therefore, it would be advantageous if the vehicle control system and the manual requests to the subsystems from the driver were integrated to allow the vehicle control system to continuously optimize the vehicle performance based on the driving terrain.
A primary purpose of any vehicle control system is to coordinate the transition of the vehicle subsystems from one set of control parameters to another set of control parameters. The vehicle control system described in EP-A-1355209 is a terrain optimization controller and includes a method of controlling a plurality of vehicle subsystems within a motor vehicle in a manner suitable for a respective driving surface. The vehicle control system pre-defines a set of planned combinations of subsystem parameters for each terrain driving mode selection available. Therefore, the vehicle performance on the terrain is optimized when these planned combinations of functionality of the subsystems occur.
However, vehicle control systems will sometimes confront circumstances where a subsystem cannot change to the pre-defined subsystem configuration mode requested. For example, in order to provide optimal performance in vehicle control system driving mode ‘A’, it is assumed that all of the subsystems are set to a corresponding ideal ‘A’ subsystem configuration mode. Instead, the vehicle control system is faced with one subsystem remaining in a ‘C’ mode while the others have changed into ‘A’ mode. Such a situation might occur when the driver manually overrides a control (e.g., the automatic transmission gearbox is in manual shifting, so the system is unable to select the appropriate shift map) or for safety reasons (e.g., the vehicle speed exceeds a threshold limit upon which it will not allow for raising the ride height). Therefore, the system may have to refuse the request to change to ‘A’ mode. Or, perhaps even more problematic is the need to retract the demand for the change to ‘A’ mode from those subsystems that have already implemented the change from the current mode. The fact that some of the subsystems might be partially changing raises the possibility of unplanned combinations of subsystem configuration modes.
Furthermore, when the vehicle control system determines that it is necessary to perform a mode change, due to the fact that control commands are issued over a serial network, the network can sometimes introduce variable latency times such that each subsystem receives the signal to change modes at different times. This latency translates into a window of time in which the vehicle is not at its' optimal performance level. Therefore, it would be advantages if the method of controlling the vehicle control system would minimize the actual time between the start and completion of a mode change so as to make negligible for all practical purposes the amount of time the vehicle is at less than optimal performance the new terrain. Moreover, it would be advantageous to provide a method of controlling a vehicle control system wherein each of the subsystems selects ‘an’ appropriate subsystem configuration mode during a transition between modes to insure that unplanned and untested combinations of subsystem configuration modes are not experienced and that the vehicle is optimized for the driving surface.
Therefore, to further improve the performance of motor vehicles including an integrated control systems as noted above, there is a need for an improved control method and apparatus which will minimize the transition time between subsystem configuration modes, avoid unplanned combinations, and maximize control of the vehicle modes when responding to a broad range of surfaces.